Culture diagnosis of meningococcal carriers: yield from different sites and influence of storage in transport medium.

Abstract

SUMMARY Different specimens and techniques have been used in the diagnosis of carriers of Neisseria meningitidis, reflecting the uncertainty about the optimal diagnostic procedure. In the present investigation the culture yield of meningococci from throat specimens was compared to that from nasopharyngeal specimens in 178 persons: 44 carriers were diagnosed. All of them were detected by culture of throat specimens while 34% of them would have remained undiagnosed if only nasopharyngeal specimens had been examined. Storage of throat specimens in a transport medium for 24 hours before culture gave a negative culture for meningococci in 41 % of the carriers. This loss was surprisingly high, the reasons for which are discussed.

Sampling methods to detect carriage of Neisseria meningitidis; literature review

“…The yield from plain swabs in Stuart's medium fell rapidly over time. Yield from charcoal swabs showed no reduction after 0e5 h and only a slight decrease after 24 h. In contrast, the study by Olcén et al 18 found a marked reduction in yield from charcoal swabs stored in transport medium for 24 h.…”

“…Olcén et al 15,18 compared the yield obtained between directly plated nasopharyngeal swabs and oropharygeal directly plated or placed in transport media. Wire, dry cotton-tipped swabs were used for nasopharyngeal sampling, dry wooden cotton-tipped swabs for direct plating and dry charcoal cotton-tipped swabs for transport media.…”

Which contacts of patients with meningococcal disease carry the pathogenic strain of Neisseria meningitidis? A population based study

“…Low levels of bacteria in the sample, loss of viability under transport, and variable sampling techniques can all influence the measured carrier rate, but sampling and transport are probably the more important factors 24. We have addressed this problem by attempting to confine sampling to two well trained members of our staff, by plating samples directly after collection, and by sampling the throat, which has been reported to have 100% sensitivity relative to other sampling sites 25. A minority of the samples were collected by hospital and clinic staff and transported before plating.…”

Invasion by Neisseria meningitidis varies widely between clones and among nasopharyngeal mucosae derived from adult human hosts

“…There is good evidence that host factors determine partly the success of Neisseria meningitidis within the nasopharynx, as some individuals appear resistant to acquisition of carriage, whilst others carry the organism chronically or intermittently (Rake, 1934). The precise site within the nasopharynx that N. meningitidis colonizes and invades is not known, but during natural carriage, the organism can be isolated both from the nose and from the throat (Olcen et al, 1979), and can be observed by immunofluorescence deep within tonsillar tissue (Sim et al, 2000).…”